The physical background and GPS TEC processing technology for identification of ionospheric anomalies forming over seismically active zones and leading to GNSS signals degradation

The recent extended studies have demonstrated that the low latitude ionosphere is very sensitive to the anomalous electric fields generated during the most last stage of the strong earthquake preparation (few days before the seismic shock). We can mention three main types of large scale (from several hundred up to several thousand km) forming over the seismically active zones: formation of positive/negative deviation of GPS TEC from undisturbed state, modification of the shape of equatorial anomaly (crests movement, changes of crest-to-trough relation, anomaly deformation), spread-F effect due to formation of plasma bubbles. Other characteristic features of seismo-ionospheric anomalies are the magnetically conjugated effect (anomaly appears also over the area magnetically conjugated to the impended epicentral area) and longitudinal effect (asymmetry in zonal direction to the position of impending epicenter) (S. A. Pulinets, International Journal of Geophysics, doi:10.1155/2012/131842, 2012).